1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs a sheet folding process and an image forming system.
2. Description of the Related Art
Conventionally, there are well-known various kinds of sheet processing apparatuses that process a bundle of plural sheets, discharged from an image forming apparatus such as a printer, a copying machine, and a facsimile machine. The sheet processing apparatus includes a stacking portion on which the sheet is stacked, and has a function of collectively performing the folding process to perform a bookbinding process when a sheet bundle is formed by the plural sheets. For example, US Patent Application Publication No. 2007/0045921 discusses a sheet processing apparatus.
The sheet processing apparatus discussed in US Patent Application Publication No. 2007/0045921 moves a lower stopper of the stacking portion to support the folding process during the sheet bundle folding process. According to the sheet processing apparatus of US Patent Application Publication No. 2007/0045921, an alignment property is improved because a folding position can be adjusted according to a size of the sheet bundle.
However, in the sheet processing apparatus of US Patent Application Publication No. 2007/0045921, the folding process is performed without fixing the sheet bundle when the sheet bundle folding process is performed. Therefore, the sheet bundle is folded while four sides of the sheet bundle vary during the folding process, and possibly quality of bookbinding state is degraded.